Step 1: Urease converts urea + water into ammonium carbamate (unstable, short-lived).
Step 2: Carbamate further hydrolyses with water to form ammonium carbonate.
Step 3: Ammonium carbonate is the relatively stable product, it slowly breaks down to release \( \text{NH}_3 \) and \( \text{CO}_2 \).
Step 4: The correct answer is \[ \boxed{\text{Ammonium carbonate}} \]